Abstract Dental caries resembles other bacterially produced diseases but differs from them in that the organisms concerned live outside the body (in the mouth), that they need not invade tissues but simply grow passively into cavities produced by their own products, and that they cause their damage not by exotoxins, endotoxins, or allergic phenomenon, but simply by the acid they produce as a metabolic product. The dentobacterial plaque is the microcosm in which the guilty organisms colonize. It is a complex organization of different bacterial types living in a “social” group. Actinomycetes appear to form its framework but various bacilli, cocci, and other forms may be found within its limits. There is no evidence that dental caries is a specific bacterial disease but rather good evidence indicates that it is a bacterial disease. In the present state of knowledge it appears that any one or group of acidogenic organisms that can maintain themselves in the environment of the dentobacterial plaque is capable of participating as an etiologic agent in the process of dental caries.